1) Field of the Invention
The invention relates to ceramic "flash TV evaporators", hereafter also referred to as "flashers".
2) Background Art
Flashers are used for the evaporation coating of monochrome or color cathode ray tubes with aluminium, in order to produce an electrically conductive layer measuring from a few hundred nanometers in the cathode ray tubes. This layer represents the electrode for accelerating the electrons in the cathode ray tube once it has been manufactured.
The dimensions of the flashers are generally 4*6*110 mm. The flasher 1 has a cavity 2 which is rectangular in the cross section of the flasher (see FIG. 1c). The cavity generally has a size of 2*4*40 or 60 mm. In the evaporation coating system, the flasher is clamped between two steel plates 6 with the aid of two screws 5. The steel plates are connected to a current source 8 via copper cables 7. To improve contact, there is generally a graphite sheet 9 between each steel plate and the flasher 1 (see FIG. 1a). The width to which it is clamped laterally at each end is about 15 mm. The length of the flasher to be heated is normally 80 mm.
The cathode ray tubes are evaporation coated as follows:
A piece of aluminium (&lt;100 mg), generally a cylindrical Al body, or pellet, is put in the cavity of the flasher. The cathode ray tube covering which is to be evaporation coated is positioned over the flasher. The space below the cathode ray tube covering is then evacuated, so that the flasher with the clamping system is contained in this vacuum (10.sup.-5 mbar).
By a direct passage of current, the flasher is heated and the aluminium contained in its cavity is evaporated. The time required for this process is in the region of 40 sec to 2 min. The current densities involved briefly reach values of up to 10.sup.3 A/cm.sup.2.
This heavy electrical and therefore thermal loading is what limits the life, i.e. number of heating cycles, of the flasher.
The flasher usually cracks in the region of the cavity after 500-900 heating cycles. It becomes broken and needs to be replaced.
The object of the invention is to provide a flash TV evaporator for the evaporation coating of cathode ray tubes with aluminium, which has an extended life, more defined behavior in terms of the evaporation of aluminium, improved wetting behavior and being nevertheless usable in conventional evaporator systems.